TABLE OF CONTENTS It is recommended that a safety factor be applied to take account of both uncertainty in the data and inaccuracy in the calculation methods.
It is assumed in the following discussion that (1) the designer has chosen a method appropriate to the application, intended to tend towards oversizing the relief system rather than the reverse, and (2) the relief system consists at most of a safety valve or bursting disc preceded by a constant diameter pipe and followed by a constant diameter pipe to atmosphere. It is also assumed that the flow through any safety valve has been checked against the manufacturer s data; under no circumstances should the mass flow be assumed to exceed the value so calculated.
The safe case is that which corresponds with the highest estimate of the required relief rate(s) and the lowest estimate of the actual flow(s).
The overall safety factor can be applied in one of two ways:
by sizing the relief system to pass a flow equal to the required mass flow multiplied by the safety factor; or
in cases where the vent capacity is determined by one particular cross-sectional area, by multiplying the calculated required vent area by the safety factor. However, it is important then to check that the capacity remains determined by this area.
The overall safety factor F 0 may be represented as the product of a number of sub-factors, each taking...
